Nerve in the context of Peritoneum

The neck is the part of the body in many vertebrates that connects the head to the torso. It supports the weight of the head and protects the nerves that transmit sensory and motor information between the brain and the rest of the body. Additionally, the neck is highly flexible, allowing the head to turn and move in all directions. Anatomically, the human neck is divided into four compartments: vertebral, visceral, and two vascular compartments. Within these compartments, the neck houses the cervical vertebrae, the cervical portion of the spinal cord, upper parts of the respiratory and digestive tracts, endocrine glands, nerves, arteries⁣⁣ and veins. The muscles of the neck, which are separate from the compartments, form the boundaries of the neck triangles.

In anatomy, the neck is also referred to as the cervix or collum. However, when the term cervix is used alone, it often refers to the uterine cervix, the neck of the ⁣⁣uterus⁣⁣. Therefore, the adjective cervical can refer either to the neck (as in cervical vertebrae or cervical lymph nodes) or to the uterine cervix (as in cervical cap or cervical cancer).

Antlers are extensions of an animal's skull found in members of the Cervidae (deer) family. Antlers are a single structure composed of bone, cartilage, fibrous tissue, skin, nerves, and blood vessels. They are generally found only on males, with the exception of reindeer/caribou. Antlers are shed and regrown each year and function primarily as objects of sexual attraction and as weapons.

Anal sex or anal intercourse principally means the insertion and thrusting of the erect penis into a person's anus, or anus and rectum, for sexual pleasure. Other forms of anal sex include anal fingering, the use of sex toys, anilingus, and pegging. Although anal sex most commonly means penile–anal penetration, sources sometimes use anal intercourse to exclusively denote penile–anal penetration, and anal sex to denote any form of anal sexual activity, especially between pairings as opposed to anal masturbation.

While anal sex is commonly associated with male homosexuality, research shows that not all homosexual men engage in anal sex and that it is not uncommon in heterosexual relationships. Types of anal sex can also be part of lesbian sexual practices. People may experience pleasure from anal sex by stimulation of the anal nerve endings, and orgasm may be achieved through anal penetration – by indirect stimulation of the prostate in men, indirect stimulation of the clitoris or an area in the vagina (sometimes called the G-spot) in women, and other sensory nerves (especially the pudendal nerve). People may also find anal sex painful, sometimes extremely so, which may be due to psychological factors in some cases.

In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes that impact the body, then works in tandem with the endocrine system to respond to such events. Nervous tissue first arose in wormlike organisms about 550 to 600 million years ago. In vertebrates, it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS consists mainly of nerves, which are enclosed bundles of the long fibers, or axons, that connect the CNS to every other part of the body. Nerves that transmit signals from the brain are called motor nerves (efferent), while those nerves that transmit information from the body to the CNS are called sensory nerves (afferent). The PNS is divided into two separate subsystems, the somatic and autonomic nervous systems. The autonomic nervous system is further subdivided into the sympathetic, parasympathetic and enteric nervous systems. The sympathetic nervous system is activated in cases of emergencies to mobilize energy, while the parasympathetic nervous system is activated when organisms are in a relaxed state. The enteric nervous system functions to control the gastrointestinal system. Nerves that exit from the brain are called cranial nerves while those exiting from the spinal cord are called spinal nerves.

The nervous system consists of nervous tissue which, at a cellular level, is defined by the presence of a special type of cell, called the neuron. Neurons have special structures that allow them to send signals rapidly and precisely to other cells. They send these signals in the form of electrochemical impulses traveling along thin fibers called axons, which can be directly transmitted to neighboring cells through electrical synapses or cause chemicals called neurotransmitters to be released at chemical synapses. A cell that receives a synaptic signal from a neuron may be excited, inhibited, or otherwise modulated. The connections between neurons can form neural pathways, neural circuits, and larger networks that generate an organism's perception of the world and determine its behavior. Along with neurons, the nervous system contains other specialized cells called glial cells (or simply glia), which provide structural and metabolic support. Many of the cells and vasculature channels within the nervous system make up the neurovascular unit, which regulates cerebral blood flow in order to rapidly satisfy the high energy demands of activated neurons.

A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the organs of the body, produce red and white blood cells, store minerals, help regulate acid-base homeostasis, provide structure and support for the body, and enable mobility and hearing. Bones come in a variety of shapes and sizes and have complex internal and external structures.

Bone tissue (also known as osseous tissue or bone in the uncountable) is a form of hard tissue, specialised connective tissue that is mineralized and has an intercellular honeycomb-like matrix, which helps to give the bone rigidity. Bone tissue is made up of different types of bone cells: osteoblasts and osteocytes (bone formation and mineralisation); osteoclasts (bone resorption); modified or flattened osteoblasts (lining cells that form a protective layer on the bone surface). The mineralised matrix of bone tissue has an organic component of mainly ossein, a form of collagen, and an inorganic component of bone mineral, made up of various salts. Bone tissue comprises cortical bone and cancellous bone, although bones may also contain other kinds of tissue including bone marrow, endosteum, periosteum, nerves, blood vessels, and cartilage.

The tongue is a muscular organ in the mouth of a typical tetrapod. It manipulates food for chewing and swallowing as part of the digestive process, and is the primary organ of taste. The tongue's upper surface (dorsum) is covered by taste buds housed in numerous lingual papillae. It is sensitive and kept moist by saliva and is richly supplied with nerves and blood vessels. The tongue also serves as a natural means of cleaning the teeth. A major function of the tongue is to enable speech in humans and vocalization in other animals.

The human tongue is divided into two parts, an oral part at the front and a pharyngeal part at the back. The left and right sides are also separated along most of its length by a vertical section of fibrous tissue (the lingual septum) that results in a groove, the median sulcus, on the tongue's surface.

Cranial nerves are nerves that emerge directly from the brain, including the brainstem. They relay information between the brain and various parts of the body, primarily to the head and neck regions and are responsible for special senses of vision, taste, smell, and hearing.

The cranial nerves emerge from the central nervous system above the level of the first vertebra of the vertebral column. Each cranial nerve is paired and is present on both sides.

A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the corresponding cervical, thoracic, lumbar, sacral and coccygeal regions of the spine. There are eight pairs of cervical nerves, twelve pairs of thoracic nerves, five pairs of lumbar nerves, five pairs of sacral nerves, and one pair of coccygeal nerves. The spinal nerves are part of the peripheral nervous system.

A body plan, Bauplan (pl. German: Baupläne), or ground plan is a set of morphological features common to many members of a phylum of animals. The vertebrates share one body plan, while invertebrates have many.

This term, usually applied to animals, envisages a "blueprint" encompassing aspects such as symmetry, layers, segmentation, nerve, limb, and gut disposition. Evolutionary developmental biology seeks to explain the origins of diverse body plans.

Cephalization is an evolutionary trend in bilaterian animals that, over a sufficient number of generations, concentrates the special sense organs and nerve ganglia towards the front of the body where the mouth is located, often producing an enlarged head. This is associated with the animal's movement direction and bilateral symmetry. Cephalization of the nervous system has led to the formation of a brain with varying degrees of functional centralization in three phyla of bilaterian animals, namely the arthropods, cephalopod molluscs, and vertebrates. Hox genes organise aspects of cephalization in the bilaterians.

The peripheral nervous system (PNS) is one of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside the brain and the spinal cord. The main function of the PNS is to connect the CNS to the limbs and organs, essentially serving as a relay between the brain and spinal cord and the rest of the body. Unlike the CNS, the PNS is not protected by the vertebral column and skull, or by the blood–brain barrier, which leaves it exposed to toxins.

The peripheral nervous system can be divided into a somatic division and an autonomic division. Each of these can further be differentiated into a sensory and a motor sector. In the somatic nervous system, the cranial nerves are part of the PNS with the exceptions of the olfactory nerve and epithelia and the optic nerve (cranial nerve II) along with the retina, which are considered parts of the central nervous system based on developmental origin. The second cranial nerve is not a true peripheral nerve but a tract of the diencephalon. Cranial nerve ganglia, as with all ganglia, are part of the PNS. The autonomic nervous system exerts involuntary control over smooth muscle and glands.

An itch (also known as pruritus) is a sensation that causes a strong desire or reflex to scratch. Itches have many similarities to pain, and while both are unpleasant sensory experiences, their behavioral response patterns are different. Pain creates a withdrawal reflex, whereas itches lead to a scratch reflex.

Unmyelinated nerve fibers for itches and pain both originate in the skin. Information for them is conveyed centrally in two distinct systems that both use the same nerve bundle and spinothalamic tract.

A nerve fascicle is a bundle of nerve fibers belonging to a nerve in the peripheral nervous system. A nerve fascicle is also called a fasciculus, as is a nerve tract in the central nervous system.

A nerve fascicle is enclosed by perineurium, a layer of fascial connective tissue. Each enclosed nerve fiber in the fascicle is enclosed by a connective tissue layer of endoneurium. Bundles of nerve fascicles are called fasciculi and are constituents of a nerve trunk. A main nerve trunk may contain a great many fascicles enclosing many thousands of axons.

Nervous tissue, also called neural tissue, is the main tissue component of the nervous system. The nervous system regulates and controls body functions and activity. It consists of two parts: the central nervous system (CNS) comprising the brain and spinal cord, and the peripheral nervous system (PNS) comprising the branching peripheral nerves. It is composed of neurons, also known as nerve cells, which receive and transmit impulses to and from it, and neuroglia, also known as glial cells or glia, which assist the propagation of the nerve impulse as well as provide nutrients to the neurons.

Nervous tissue is made up of different types of neurons, all of which have an axon. An axon is the long stem-like part of the cell that sends action potentials to the next cell. Bundles of axons make up the nerves in the PNS and tracts in the CNS.

Vasculitic neuropathy is a peripheral neuropathic disease. In a vasculitic neuropathy there is damage to the vessels that supply blood to the nerves. It can be as part of a systemic problem or can exist as a single-organ issue only affecting the peripheral nervous system (PNS). It is diagnosed with the use of electrophysiological testing, blood tests, nerve biopsy and clinical examination. It is a serious medical condition that can cause prolonged morbidity and disability and generally requires treatment. Treatment depends on the type but it is mostly with corticosteroids or immunomodulating therapies.

Peripheral neuropathy, often shortened to neuropathy, refers to damage or disease affecting the nerves. Damage to nerves may impair sensation, movement, gland function, and/or organ function depending on which nerve fibers are affected. Neuropathies affecting motor, sensory, or autonomic nerve fibers result in different symptoms. More than one type of fiber may be affected simultaneously. Peripheral neuropathy may be acute (with sudden onset, rapid progress) or chronic (symptoms begin subtly and progress slowly), and may be reversible or permanent.

Common causes include systemic diseases (such as diabetes or leprosy), hyperglycemia-induced glycation, vitamin deficiency, medication (e.g., chemotherapy, or commonly prescribed antibiotics including metronidazole and the fluoroquinolone class of antibiotics (such as ciprofloxacin, levofloxacin, moxifloxacin)), traumatic injury, ischemia, radiation therapy, excessive alcohol consumption, immune system disease, celiac disease, non-celiac gluten sensitivity, or viral infection. It can also be genetic (present from birth) or idiopathic (no known cause). In conventional medical usage, the word neuropathy (neuro-, "nervous system" and -pathy, "disease of") without modifier usually means peripheral neuropathy.

Anilingus (also spelled analingus) is an oral and anal sex act (anal–oral contact or anal–oral sex) in which one person stimulates the anus of another by using their tongue or lips.

The anus has a relatively high concentration of nerve endings and can be an erogenous zone, and so the recipient may receive pleasure from external anal stimulation, whereas pleasure for the giver is usually based more on the principle of the act. People may engage in anilingus for its own sake, before anal penetration, or as part of foreplay. All sexual orientations may participate in the act. Studies confirm anilingus to be one of the sexual practices between women, though only practiced by a minority.

In amniotes, the clitoris (/ˈklɪtərɪs/ KLIT-ər-iss or /klɪˈtɔːrɪs/ klih-TOR-iss; pl.: clitorises or clitorides) is a female sex organ. In humans, it is the vulva's most erogenous area and generally the primary anatomical source of female sexual pleasure. The clitoris is a complex structure, and its size and sensitivity can vary. The visible portion, the glans, of the clitoris is typically roughly the size and shape of a pea and is estimated to have more than 10,000 nerve endings.

Sexological, medical, and psychological debate has focused on the clitoris, and it has been subject to social constructionist analyses and studies. Such discussions range from anatomical accuracy, gender inequality, female genital mutilation, and orgasmic factors and their physiological explanation for the G-spot. The only known purpose of the human clitoris is to provide sexual pleasure.

A sensory nerve, or afferent nerve, is a nerve that contains exclusively afferent nerve fibers. Nerves containing also motor fibers are called mixed. Afferent nerve fibers in a sensory nerve carry sensory information toward the central nervous system (CNS) from different sensory receptors of sensory neurons in the peripheral nervous system (PNS).

Contrarily, a motor nerve carries information from the CNS to the PNS.